Electrolytically deburring moving strip

ABSTRACT

Trimmed edges of moving metallic strip are electrolytically deburred. Resulting strip is suitable for hot-dip coating or electroplating.

United States Patent 1111 3,803,014

Atkinson v Apr. 9, 1974 [54] ELECTROLYTICALLY DEBURRING 2,341,158 2/1944Nachterran 204/206 2,971,810 2/ l 961 Ressler MOVING STRIP I 3,527,6789/1970 Suzuki 204/15 [75] Inventor: Edward S. Atkinson, M1ch1gan City,3, 9, 972 r r et Ind. 3,467,593 9/1969 Dickson et al. 204/224 M [73]Assignee: National Steel Corporation,

Pittsburgh, Pa.

Primary E.\'uminerF. C. Edmunds e Filed; 1972 Attorney, Agent, orFirm-Shanley & ONeil 211 Appl. No.: 299,736

52 u.s.c1. 204/206, 204/129.1 51 1111.01 B23p 1/02 [57] ABSTRACT [58]Field of Search 204/1295, 129.55, 129.6, Y

204/129.65, 224 M, 206-21 1, DIG, 7 Trimmed edges of moving metallicstrip are electrolytically deburred. Resulting strip is suitable forhot-dip [56] References Cit d coating or electroplating.

UNITED STATES PATENTS 893,814 7/1908 Schmitz 204/206 10 Claims, 4Drawing Figures ELECTROLYTICALLY DEBURRING MOVING STRIP BACKGROUND OFTHE INVENTION This invention relates to treatment of metallic stripprevious to hot-dip coating or electroplating.

In typical manufacture of steel strip suitable for coating (zinc, temeand aluminum are common hot-dip metals) or plating (tin, chromium orzinc are common platings), slabs are rolled at elevated temperatures toproduce hot rolled strip which in turn is pickled, cold rolled, andannealed. The hot rolled strip is sometimes slit to produce narrowerwidths. The cold rolled strip is often continuously side-trimmed toestablish accurate and uniform width and to produce parallel edges. Suchslitting and trimming leaves a longitudinal edge with a downwardlyextending thin, sharp fin or ridge. Slitting leaves one or two suchedges and trimming leaves two such edges. The term trimming is usedhereinafter to include both slitting and trimming and the ridgeresulting from either is denoted side-trim burr. Such burr isundesirable because it causes a heavy edge coating in any subsequenthot-dip or plating process. Also the burr can damage strip processingapparatus.

It is known to mechanically treat side-trim burr thereby obviating theseproblems. Mechanical deburring is accomplished by ploughs which arecircular knives arranged at an angle to the edge of the strip such thatthe knife edges shear off the burr. They are usually used in conjunctionwith masher rolls. These are coneshaped rolls which mash the remainderof the burr flat. Mechanical deburring is difficult and involvesconsiderable maintenance problems relating to the knives.

The main object of this invention is the provision of a deburring systemin which the difficulties and maintenance problems associated withmechanical deburring are overcome.

Other objects of the invention will appear from the following detaileddescription.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 schematically illustrates adeburring system embodying principles of the present invention.

FIG. 2 is a cross-sectional view on line 2-2 of FIG. 1.

FIG. 3 is a view of a portion of the view of FIG. 2. FIG. 4 is across-sectional view illustrating alternative apparatus within the scopeof the invention in conjunction with a portion of a strip to bedeburred.

DETAILED DESCRIPTION With references to FIGS. l-3, a tank defines acontainer having a bottom wall 12, a top wall 13, a back side wall 14, afront side wall (not shown), an end wall 16 and an end wall 18. The endof tank 10 near end wall 16 is denoted the strip entrance end. The endof tank 10 near end wall 18 is denoted the strip exit end. An enclosure20 communicates with the interior of tank 10 through top wall 13 at thestrip entrance end and enclosure 22 communicates with the interior oftank 10 through top wall 13 at the strip exit end. Enclosure 20 has aninlet 24 outside tank 10 and an outlet 26 in the interior of tank 10.Enclosure 22 has an inlet 28 in the interior of tank 10 and an outletoutside tank 10 (not shown). A conduit 30 having a valve 82 communicateswith the interior of tank 10 through end wall 18. The tank 10 is adaptedto contain a bath 34 of electrolyte.

A travel path 36 for movement of metallic strip through tank 10comprises a conductor roll 38 outside tank 10 and within enclosure 20, asink roll 40 within tank 10 at its strip entrance end, a tensioning roll41 within tank 10 toward its strip exit end positioned lower than roll40, a sink roll 42 within tank 10 at its strip exit end positioned lowerthan roll 40 but higher than roll 41, and an exit roll 44 outside tank10 and in enclosure 22. Thus, conductor roll 38 is upstream of the stripentrance end of tank 10 and exit roll 44 is downstream of the strip exitend of tank 10.

Positioned within tank 10 on each side of travel path 36 is an electrode46 (see FIG. 2). Each electrode 46 is positioned to establish a workinggap 48 (see FIG. 3) between the electrode and the burr on an adjacentedge of strip moving along the travel path 36.

Conductor roll 38 is electrically connected to the positive side of agenerator 50 (or other suitable source of electric power) and electrodes46 are electrically connected to the negative side of generator 50.

A lower guide roll 52 which is outside of tank 10 and of enclosure 20near the strip entrance end and an upper guide roll 54 within enclosure20 upstream of conductor roll 38 provides means for guiding strip totravel path 36.

In operation, metallic strip 56 having opposite trimmed longitudinaledges which are to be deburred continuously passes under guide roll 52,enters enclosure 20 through inlet 24, and passes over guide roll 54,over conductor roll 38, and through outlet 26 into tank 10 and intoelectrolyte bath 34. The strip then passes under sink roll 40, pastelectrodes 46, over tensioning roll 41, under sink roll 42, out of thebath of electrolyte, into inlet 28 of enclosure 22, out of tank 10, overexit roll 44 and then out of enclosure 22. Thus, strip 56 followstravelpath 36 through tank 10 and through the bath of electrolyte in the tank.

Since the electrodes 46 are positioned on each side of the travel pathwithin bath 34, an electrode 46 is po sitioned within the bath adjacenteach longitudinal edge of the strip 56 to establish a working gap 48(FIG. 3) between the electrode and the burr on an adjacent edge of thestrip.

Conductor roll 38 imparts a positive potential to strip 56 passing overit so that the strip 56 functions as an anode. The electrical connectionfrom the negative side of generator 50 imparts a negative potential toeach of the electrodes 46. As a result, an electric circuit is formedbetween the strip 56 and each electrode 46 so that current can flowthrough the electrolyte of bath 34 which is present in each working gap48.

The potential difference, that is the voltage, and the working gap aresuch as to obtain electrochemical machining action at each longitudinaledge of the strip to remove side trim burr 57. After washing, the stripis suitable for hot-dip coating or electroplating. The removedmetal'either reacts chemically to form a sludge or reacts chemically togo into solution depending on the electrolyte as discussed in detaillater. Hydrogen released at the electrodes and oxygen released at thestrip edge are vented from the apparatus through ductwork (not shown)communicating with the interior of tank 10 through top wall 13.

Usually the strip 56 is passed through tank at a speed consistent withthe speed of the strip through other processing steps, for example,cleaning or coating. If a speed can be utilized independent of the speedof the strip through other processing steps, a speed is selected so thatwith the length 58 (FIG. 1) of the electrodes46 and the voltage andworking gap which are desired to be utilized, a desired amount ofdeburring will occur. Increased strip speed can be compensated for byincreased electrode length, increased voltage or reduced working gapwhile decreased strip speed can be compensated for by decreasedelectrode length, decreased voltage or increased working gap. Ingeneral,

strip speeds which are usually utilized range from about 100 feet perminute to about 2,500 feet per minute.

The electrolyte is one suitable for the electrochemical machining of themetal being processed. Such electrolytes are described at pages 234 and235 of Volume 3 of the Metals Handbook (eighth Edition). Preferably, asludging electrolyte is utilized. With these electrolytes, theanodically removed metal reacts to produce an insoluble product denotedsludge. An example of a very suitable sludging electrolyte is an aqueoussodium chloride solution. If a sludging electrolyte is used, rolls 40,41 and 42 should be positioned sufficiently above the bottom wall 12 oftank 10 so thatthe sludge formed during processing will build up to alevel where it interferes with the strip or electrodes only after arelatively long period of time so that sludge removal will only have tobe carried out infrequently. Non-sludging electrolytes can also be used.These retain the removed metal in solution and do not produce a sludgeunder electrochemical machining conditions; but, a larger content ofdissolved metal gives a greater tendency for metal to plate out ofsolution on the electrodes.

Besides being dependent on time of exposure of an edge of the strip toan electrode which is dependent upon electrode length and strip speed,deburring action, that is, metal removal, is dependent upon currentdensity. The current density is a viariable of potential difference(voltage) and working gap. With the present process and apparatus, the.current density tends to concentrate in the side trim burr; as a result,there will be a greater tendency for the removal of the side trim burrthan for the removal of other portions of the strip.

A preferred current density is readily established by trial and error byvarying the voltage or working gap and noting the deburring results todefine the particular voltage and working gap most suitable for aparticular typeof strip. If the current density is too low, all the burrwill not be removed though the sharpest edges of the burr will be dulledto achieve some advantage. If the current density is too high, not onlywill the entire burr be removed, but metal will be removed from the.edge of the strip resulting in inefficiency though this will not befatal to the operativeness of the system. Current density can beincreased by increasing the voltage or decreasing the working gap.Current density can be decreased by decreasing the voltage or increasingthe working gap. I

Usually, a voltage in the range of 4 to 30 volts dc will be suitable.

The working gap is defined for convenience herein in terms of thespacing of the extreme end of the burr and the nearest point on theexposed conductive portion of the electrode to which it is adjacent. Asuitable working gap for use in the present invention has such a spacingranging from one-thirtysecond of an inch to about 1 inch. Preferably,such spacing ranges from onesixteenth of an inch to one-half inch.

Turning now to a description of the electrodes, it is preferred thatthese have a configuration and construction which gives the greatestcurrent density at the burr of the adjacent strip edge. Such occurs whenthe electrodes have an exposed conductive portion conforming to a stripedge to be deburred.

FIG. 2 shows such an electrode. It has a C-shaped exposed conductivesurface which defines an elongated slot 62 for receiving a strip edge.Deburring will occur regardless of the upward or downward orientation ofthe burr. In trimming as described hereinbefore the burr is all orienteddownwardly because of the nature of the trimming process; however, ifthe strip is recoiled prior to deburring, the burr can face eitherupwardly or downwardly as the strip passes through the electrolyte bathadjacent the electrode depending upon how the strip was recoiled. Thus,the C-shaped electrodes depicted in FIG. 2 are highly desirable sincethey obviate coiling in a particular way to achieve deburring results.

FIG. 4 shows an electrode with an inverted L-shaped active conductivesurface. With this electrode, the strip must be oriented with the burrfacing upwardly. An upright L-shaped electrode can be utilized where theburr faces downwardly.

It is highly preferred that the portion of the electrode to besubmerged, except for the surface adjacent the portion of the strip tobe deburred, that is except for the slot receiving the strip in the caseof the C-shaped electrode, is enclosed by rubber, polyvinyl chloride, orother electric insulating substance. This reduces or avoids removal ofmetal other than the burr from the strip so that the strip does notdepart from permitted tolerances and uniform results are achieved. Suchinsulation is denoted by reference numeral 63a.

So far as the conductive portion 63b of the electrode is concerned, anygood conductor of electricity which is compatible with the electrolytebath under conditions of deburring is satisfactory. Preferred materialsare copper or stainless steel.

With reference to FIG. 1, the electrodes are mounted on carriers 64.With references to FIGS. 1-4, a passageway 66 extends through theinterior of each carrier 64 and through the interior of each electrode46 having an outlet 68 opposite the strip edge to be deburred. Eachpassageway 66 communicates at its inlet with a conduit 70. Duringoperation electrolyte is introduced continuously through conduits 70andpassageways 66 exiting outlets 68 so that it impinges against theadjacent strip edge. Such impingement prevents the sticking ofprecipitate to the strip and causes circulation of the electrolytethereby controlling undesired heat buildup. Such circulation also hasthe advantage of moving gas bubbles from the area of the strip edge sothat such bubble removal is regular resulting in more uniformprocessing.

The continuous addition of the electrolyte makes up for drag-out ofelectrolyte on the strip leaving tank 10. Conduit 30 and valve 82(FIG. 1) are provided to remove electrolyte from the tank should suchremoval be necessary or desired. Such electrolyte may be recirculatedafter removal of entrained particles.

It is highly preferred that strip flutter be minimized. This reduces thepossibility of the electrode and strip touching resulting in arcing andburning of the strip. To this end, the strip 56 is deflected over roll41 so as to produce tension on the strip and the rolls 40, 41 and 42have relatively large diameters (e.g. 1 foot) and are relativelypositioned so that the span between the rolls 40 and 41 is minimized andranges for example from 2 to 5 feet as measured along the travel path.

It is also highly preferred that the lateral alignment of the strip withrespect to the electrode be maintained. This also reduces thepossibility of the electrode and the strip touching resulting in arcingand burning of the strip.

FIG. 1 shows apparatus for maintaining such alignment. Within enclosure20 and outside of tank means to detect lateral misalignment of the stripis shown in the form of a photoelectric device 71 comprising a lightsource 72 at each edge of the strip that directs light toward a detectorunit 74, each associated light source and detector unit being positionedso that the edge of the strip intercepts a light beam on that side ifthe strip becomes misaligned in that direction. If desired, the stripcan normally intercept the light beams with misalignment being indicatedby a light beam getting through to a detector unit. In either case asignal is generated or terminated to indicate misalignment. The detectorunits 74 are electrically connected to a strip steering unit 76 which inresponse to detection of lateral misalignment corrects the misalignmentby steering the strip.

Units for steering strip in response to detection of strip edgemisalignment are well known and commercially obtainable. Some of theseinstead of responding by detecting by photoelectric means respond todetecting by pneumatic or other means. For examples of strip steeringunits disclosed in patents of the assignee of the present application,see US. Pat. Nos. 3,175,813 and 3,188,063. Patents of an assignee fromwhom strip guide control systems are commercially available are US. Pat.Nos. 3,039,483; 3,533,542; 3,586,904 and 3,570,735. For an example of astrip guide control unit for an electroplating apparatus see NachtmanU.S. Pat. No. 2,341,158.

instead of a detector 74 sending a signal to a steering unit, thedetector 74 can send a signal via an electrical connection to a motor 78which moves the electrodes 46 in respnse to a signal from 74 to maintainthe electrodes spaced from the strip.

A combination of strip steering and electrode moving can also beutilized.

A specific operating example follows: the apparatus shown in FIGS. 1-3is utilized. The tank 10 has depth of 3 feet and a width of 90 inches.The rolls 40, 41 and 42 each have diameters of 1 foot and the distancebetween rolls 40 and 41 as measured along the travel path is about 4.5feet. The tank 10 contains an aqueous sodium chloride electrolytecontaining 2 pounds of sodium chloride per gallon of water. Side trimmed48 inch wide steel strip is passed through the reservoir at a stripspeed of 180 feet per minute. A working gap is utilized having a spacingas hereinbefore defined of one-eighth inch. The lateral alignment of thestrip is maintained utilizing a strip steering unit responsive to aphotoelectric strip edge detector which is outside the tank. Eachelectrode has a length of 3 feet. A dc potential difference of 18 voltsis applied. Substantially complete deburring is achieved withsubstantially no removal of other metal from the edge of the strip.After washing, the strip is readily coated or plated without the heavyedge buildup normally associated with the coating of strip which has notbeen deburred.

While the above embodiment is described in terms of the use of twoelectrodes deburring opposite longitudinal edges, the invention isintended to encompass apparatus with a single electrode or multipleelectrodes deburring a single edge.

Thus, the above is to be considered in all respects as illustrative andnot restrictive, the scope of the invention being indicated by theappended claims rather than the foregoing description, and all changeswhich come within the meaning and range of equivalency of the claims aretherefore intended to be embraced therein.

What is claimed is:

1. Apparatus for deburring a trimmed edge of moving metallic stripcomprising a. means defining a container for a bath of electrolyte,

b. means defining a travel path for the metallic strip through thecontainer,

c. electrode means positioned within the container on at least one sideof the travel path to establish a warking gap between said electrodemeans and an adjacent edge of the strip moving along the travel path,said electrode means having an exposed conductive portion configured andpositioned so as to be opposite both said strip edge and also a marginalportion of at least one strip surface adjacent said edge, and means forimparting a positive potential to the strip and means to impart anegative potential to said electrode means to form an electric circuitbetween the strip and the electrode means so that current can flowthrough electrolyte which is present in each working gap to remove sidetrim burr by electrochemical machining action.

2. Apparatus of claim 1 which additionally comprises means forminimizing strip flutter.

3. Apparatus of claim 2 wherein the means for minimizing strip fluttercomprises tensioning means.

4. Apparatus of claim 1 which additionally comprises means outside thecontainer for maintaining the lateral alignment of the strip within thecontainer.

5. Apparatus of claim 4 wherein the alignment maintaining meanscomprises means to detect lateral misalignment of the strip and meansresponsive to the detection to correctthe misalignment.

6.-Apparatus of claim 1 wherein the electrode means has a configurationand construction which gives the greatest current density at the burr ofthe adjacent strip edge.

7. Apparatus of claim 6 wherein the electrode means has a C-shapedexposed conductive portion which defines an elongated slot for receivingthe adjacent strip edge.

8. Apparatus of claim 7 wherein the portion of the electrode to besubmerged is enclosed by insulation except for the slot receiving thestrip.

9. Apparatus of claim 1 wherein the electrode means contains apassageway for the introduction of electrolyte into the container withmeans forming an opening designed to impinge the electrolyte against theadjacent strip edge.

10. Apparatus of claim 6 wherein the electrode means has an L-shapedexposed conductive portion.

1. Apparatus for deburring a trimmed edge of moving metallic stripcomprising a. means defining a container for a bath of electrolyte, b.means defining a travel path for the metallic strip through thecontainer, c. electrode means positioned within the container on atleast one side of the travel path to establish a warking gap betweensaid electrode means and an adjacent edge of the strip moving along thetravel path, said electrode means having an exposed conductive portionconfigured and positioned so as to be opposite both said strip edge andalso a marginal portion of at least one strip surface adjacent saidedge, and d. means for imparting a positive potential to the strip andmeans to impart a negative potential to said electrode means to form anelectric circuit between the strip and the electrode means so thatcurrent can flow through electrolyte which is present in each workinggap to remove side trim burr by electrochemical machining action. 2.Apparatus of claim 1 which additionally comprises means for minimizingstrip flutter.
 3. Apparatus of claim 2 wherein the means for minimizingstrip flutter comprises tensioning means.
 4. Apparatus of claim 1 whichadditionally comprises means outside the container for maintaining thelateral alignment of the strip within the container.
 5. Apparatus ofclaim 4 wherein the alignment maintaining means comprises means todetect lateral misalignment of the strip and means responsive to thedetection to correct the misalignment.
 6. Apparatus of claim 1 whereinthe electrode means has a configuration and construction which gives thegreatest current density at the burr of the adjacent strip edge. 7.Apparatus of claim 6 wherein the electrode means has a C-shaped exposedconductive portion which defines an elongated slot for receiving theadjacent strip edge.
 8. Apparatus of claim 7 wherein the portion of theelectrode to be submerged is enclosed by insulation except for the slotreceiving the strip.
 9. Apparatus of claim 1 wherein the electrode meanscontains a passageway for the introduction of electrolyte into thecontainer with means forming an opening designed to impinge theelectrolyte against the adjacent strip edge.
 10. Apparatus of claim 6wherein the electrode means has an L-shaped exposed conductive portion.